Rotary furnace



June 7, 1938. c. P.- DEBUCH ET Al.

ROTARY FURNACE Original Filed Septll, 1934 4 Sheets-Sheet l Inventors:af/ Rau] Deb uca/2J June 7, 1938. c. P. DEBUcH ET A1.

ROTARY FURNACE original Filed sept. 11, 1954 4 sheets-sheet 2 June 7,1938. c. P. DEBUCH ET AL ROTARY FURNACE Original Filed Sept. l1, 1934 4Sheets-Sheet 3 June 7, 1938.

c. P.` DEBUCH Er Al. 2,119,528

ROTARY FUPJJACE Original Filed Sept. l1, 1934 4 Sheets-Sheet'4 Emst A1arjfw @rz/1 Patented June 7, 1938 UNITED STATES lPATENT OFFICEfort-on-the-Main,

Germany,

assignors to American Lurgi Corporation, New York, N. Y., a corporationof New York Original application September 11, 1934, Serial Divided andthis application May 12, 1936, Serial No. 79,256. In Germany May 11Claims.

The present invention relates to rotary furnaces, and, moreparticularly, to rotary furnaces of an improved character for carryingout chemical and metallurgical operations.

It is well known that the use of rotary tubular furnaces for carryingout metallurgical and chemical processes, such as roasting, have theadvantage of obtaining a large output with a single furnace. Numerousendeavors have been directed to increasing the output of the rotarytubular furnace. Many diiculties have been encountered which were duenot so much to causes in the metallurgical or chemical operations suchas the presence of an undue residual amount of sulphur in the productsobtained in roasting pyrites, but rather to the fact that when theoutput was increased beyond a certain limit, excessively hightemperatures occurred in certain zones of the furnace and lead to theformation of incrustations and to other phenomena of sintering. Variousproposals have already been suggested to overcome the difllculties ofincreasing the output of a rotary tubular furnace. Thus, attempts havebeen made to make the superficial area of the charge exposed to theatmosphere of the furnace as large as possible in relation to the weightof the material under treatment. For the purpose of carrying theseattempts into practice, turning devices have been provided in thefurnace and the bed of the ore present has been kept as shallow aspossible. The purpose of the turning mechanism was to bring the chargeinto repeated contact with the furnace atmosphere, and, it was believed,that the most advantageous depth of the charge realized by adjusting andcorrelating the angle of inclination of the furnace, the height of thebaiile rings and the revolutions of the furnace in such a manner thatthe charge passed through the furnace in about 4 to 8 hours. Althoughvarious proposals and attempts were made to solve the problemconfronting the art none, as far as is known, has been wholly successfuland satisfactory when carried into practice.

We have discovered that it is possible to increase the output of rotarytubular furnaces in a surprisingly simple way. It has been fouml thatthe quantity of charge material actually present in the furnace has adecisive influence on the operation of the furnace and on its output.

It is an object of the present invention to increase the output of arotary tubular furnace.

It is another object of the present invention to eliminate detrimentalincrustations and sinteringphenomena in a rotary tubular furnace.

It is a. further object of the invention to provide an improved rotarytubular furnace capable of retaining and treating an increased quantityof charge material.

The invention also contemplates the provision ofa furnace headpermitting accurate control of the withdrawal of furnace gases from arotary tubular furnace.

Other objects and advantages will become apparent from thefollowingldescription taken in conjunction with the accompanyingdrawings, in Which:-

Fig. 1 is a longitudinal sectional view of a rotary tubular furnace ofthe type used for carrying the present invention into practice;

Fig. 2 illustrates a similar view of a rotary tubular furnace embodyingthe present invention with baille rings of different heights;

Fig. 3 depicts the novel rotary furnace with a head at both of its endsand equipped with gas outlets opening into a chamber concentricallysurrounding the shell of the furnace.

Fig. 4 depicts a longitudinal sectional View of a similar furnace withopenings in the shell, through which gases are led from the furnace.

Fig. 5 shows a similar view of a rotary furnace of varying innerdiameter.

Fig. 6 is the sectional View of a furnace head for withdrawing gas fromthe furnace.

Fig. 7 illustrates a longitudinal sectional view of a further modifiedembodiment of the invention.

Broadly stated, the output of a rotary tubular furnace can be increasedto a substantial extent by proceeding in accordance with the principlesof the present invention. We have discovered that a substantial increasein the output of a furnace can be effected by retaining a criticallyexcessive amount of charge in the furnace. It has been found that adominant bed amounting. to at least about one-half of the daily (24hours) output of the furnace should be retained within the furnace. Suchan excessive bed not only does not interfere with carrying out themetallurgical or chemical reactions completely, but it makes it possibleto obtain new and improved results including an increased output, anecient exchange of heat between the various sections of the furnace, anincreased efficiency, a more thorough and uniform conduct of thereactions and the like.

The large and excessive quantity of material necessary for carrying thepresent method into practice may be retained in the furnace by variousmeans. Thus, for example, the angle of inof the furnace.

clination of the furnace may be decreased without modifying theconstruction of the rotary tubular furnace. It is to be preferred,however, to retain the dominant bed in the furnace by providing baillerings or plates of special height to divide the furnace into a pluralityof sections. The angle of inclination of the furnace can be eithermaintained or modified (diminished or increased) as desired. The baillerings may all be of the same height or else -of different heights inorder to control the quantity of the charge present in the individualsections of the furnace. A structural arrangement of this sort isespecially desirable for roasting sulphide ores, such as pyrites. Inthis case, the height of the baille rings may be increased eitherproportionately or according to a definite curve from the upper end orfrom the reaction zone towards the lower end When roasting sulphidicores, there are certain zones in the rotary tubular furl nace in whichthe reaction proceeds quickly, and

other Zones in which the course of the reaction is considerably moresluggish, the latter zones being in most cases situated at the lower endof the furnace. When treating sulfide ores according to the presentinvention, the height of the baille rings in the lower sections of thefurnace is increased until the amount of the charge which comes intoreaction in a unit of time is practically the same in all sections.roastingof pyrites, it has been ascertained that only half as muchsulphur is burned 01T in a unit of time in a section at the lower end ofthe furnace, raising the height of the baille rings in the section wherethe reaction is more sluggish, the

quantity of charge in this section can easily be increased to about thedouble of the quantity present in the other sections where the reactiontakes a normal course. In this manner, the quantity of material enteringinto reaction in a unit of time will be correspondingly larger becausethe speed .(velocity) of the reaction will not be changed much throughthe increase in the amount of material in that particular section. Ithas been found that the amount of sulphur burned off in a unit of timein the section under consideration Will be practically the same as' inthe other sections and the working temperature in this section willadjust itself to about the same level as in the othersections.

Generally, it is advisable to maintain constant gas velocities in rotarytubular furnaces. When carrying the present method into practice alarger amount of reactive gases than usual must be supplied to eachsection of the furnace. In some cases, this requirement ci be fulfilledonly by increasing the velocity of the gases in the furnace above thevelocity found to be the most suitable. The present invention overcomesthis difficulty and assures an adequate supply of gas to all parts ofthe furnace, by leading 'a portion of the gases through openings orports provided in the shell of the furnace and conducting them intopipes connected with said ports and located outside the furnace. Theamount of gas which is withdrawn can always be so adjusted that atpractically all times the most advantageous gas velocity is maintainedwithin the furnace.

In many cases, it is of great importance to be able to control the flowof the gases through the furnace by means of a single device. Accordingto the present invention, this can be easily accomplished, withoutinterfering with the possibility of individually controlling the severalcurrents of gas withdrawn from the furnace, by providing For example, ifin the.

'furnace head and, in case of need, also in the pipes. The annular andthe central passages in the furnace head open into the same gascompartment that houses the equipment for conveying the gas. Thisarrangement makes it possible to control accurately and independentlyeach partial gas current. Furnace heads of this type may, of course, beprovided at each end of the furnace in which case in one portion of thefurnace the` gas can be passed in the direction followed by the chargematerial, and in the,` other portion of the furnace in the oppositedirection. In addition, gas may be withdrawn through the openings orports in the shell and the flow of gas and the temperatures in allsections of the furnace can be influenced or controlled as desired. Inmany cases, however, one such furnace head will suillce. In this case,it is possible not only to operate the furnace on the parallel flow oron the counterflow principle, but also to control the flow of gas in theindividual sections of the furnace by with- Idrawing gas through theshell.

'I'he supply of gas to the furnace may be controlled in any well knownmanner, such as by means of openings at one or both ends of the furnace.In place of or in addition to said openings, of course, gas intakes maybe provided, uniformly or distributed in any other way over .the surfaceof the furnace.

In the drawings the reference character I des-v device 5, and an outlet6. Nozzles 1 are provided in the furnace for introducing air or othergases needed for reactions. Within the furnace a plurality of baillerings 8 I, 8 2, 8 3, 8 4, etc. are provided.

Referring more particularly to Fig. 1, a furnace is illustrated withbaffle rings of such dimensions as to retain as a dominant bed thedesired quantity of material. For example, a dominant bed of about 3A;to about 11/2 times the daily (24 hours) output of a furnace, which mayhave the usual angle of inclination. All of the baflie rings are of thes-ame'height and are uniformly spaced so that the sections are ofapproximately equal length and accommodate approximately equalquantities of material. The gases are Withdrawn from the furnace througha head 9. At the otherend, the furnace is closed, for example, by acover I0. This cover, if desired, may be provided with nozzles for theadmission of air or other reactive gases. A furnace of this type can beemployed to advantage, for example, for treating materials in which theconstituents undergoing conversion react at approximately the same ratein all parts of the furnace.

Fig. 2 illustrates a modified furnace which is quite similar to the oneshown in Fig. 1. 'I'he height of the baffle rings, however, increasesfrom the right hand end of the furnace to the left hand end. Thus, itwill be observed that rings 8 I, 8 2, 8 3 are rather higher than4 rings8 1, 8 8 and 8 9. Due to this arrange- `ment substantially largerquantities of the charge material are retained in sections II, I2 and I3than in sections I4, I5 and I6. v

It has been found that the modified furnace is especially suitable forroasting pyrites, zinc blends and other materials in which the reactionproceeds very rapidly at rst and much slower afterwards. When thesematerials are treated in the present furnace, the lower sections thereofhold substantially larger quantities of the charge than the uppersections and, although the reaction has a much slower rate towards thelower end of the furnace, still the amount of the material undergoingconversion and the heat liberated per unit of time will be approximatelythe same in all sections of the furnace. Similar results have beenobtained with the furnace depicted in Fig. 5 in which the diameter ofthe free space is larger towards both ends than in the center. Thisconstruction can be obtained, for example, by tapering the thickness ofthe lining from the center towards the two ends. The height of the balerings 8 is less in the upper part (right hand end) of the furnace th-anin the lower part (left hand end). The height of the lower rings is atleast such that the imaginary line passing through their upper edges isapproximately parallel to the axis of the furnace and about flush withor projecting beyond the upper edges of the baiile rings in the centralzone. By means of these arrangements, it is possible to control and varyin any desired manner, the rate of movement of the material through thedifferent zones of the furnace `and the quantity of material retained inthe various sections.

'I'he rate of the reaction in the individu-al Vsections of the furnacemay be modified, influenced or controlled by structural arrangementsshown in Figs. 3 and 4. With these arrangements the reaction iscontrolled by a suitable adjustment of the flow, velocity, and quantityof the gases in the furnace. In Fig. 3, two gas outlets are designatedby reference characters I'I and I8 which open into a chamberconcentrically surrounding the shell of the furnace. Each gas outletconsists of rotative members I9 which rotate with the furnace and astationary member 20 which is provided with a gas exhaust 2I and adevice 22 for removing the dust deposited by the gases. The furnace ofthis type permits the withdrawal of gas at a number of points, to wit:through the two furnace heads 23 and 24 and through the gas outlets I'Iand I8. The number of these gas outlets may be further increased, forexample, by providing similar gas outletsl which extend through theshell in other sections bounded by two baille rings. Y Y

By controlling the gas supply through nozzles 'I and by suitableadjustment of the control devices for the three or more gas outlets ofthe furnace, it is possible either to Withdraw equal quantities of gasof approximately the same composition through all of the gas outlets orelse to withdraw a different volume and composition of gases at eachoutlet. Obviously, the individual currents or streams of gas may bereunited outside the furnace. Each gas current or stream may beindividually put to further use or each may be treated separately orsome or all of the gas streams may be run to waste. For removing dustfrom some or all of the gas streams issuing from the furnace suitabledust separating or collecting devices may be employed. A certainquantity of dust from the gas may be deposited in the concentric chamberformed by the members I9 and 20. For' the purpose of removing lupper endof the gas main 45.

the thus deposited dust, the chamber is provided with a dust outlet 22having a removable cover.

The rotary tubular furnace illustrated in Fig. 4 is provided with one ormore openings or ports 25 in the shell through which the gases are ledfrom the furnace. These openings may be incorporated in several sectionsof the furnace or kiln. The gases issuing from the furnace through .saidopenings are conducted by pipes 26 to a furnace head 21 in which theyare re-united with the gases flowing directly to the head from thefurnace.

Fig. 'T illustrates a longitudinal sectional view of another modiedembodiment of the invention into a rotary tubular furnace. This furnaceis similar to the one shown in Fig. 4 with the difference, however, thata furnace -head is provided at each end of the furnace shell, saidfurnace heads being denoted by reference characters 23-I and 24-I,respectively. Openings 25-I are provided in the furnace shell, and, sameas in Fig. 4, the gases issuing from the intermediate compartments ofthe furnace through said openings are conducted by pipes 26-I to furnaceheads 23-I and 24-I in which they are re-united with the gases flowingdirectly to the furnace heads and are withdrawn from the furnace.

In all embodiments control or closure members or valves are provided ineach inlet, outlet, pipe, etc. through which gases flow. The memberspermit each device for admitting or withdrawing the gases to bethrottled or completely closed or v opened as desired.

In the event that the pipes conveying the gases drawn from the furnacethrough openings located in the shell open into a furnace head, it isadvisable to provide an additional control device in the openings orports.

An appropriate control device is illustrated in detail in Fig. 6. Theupper end of the rotary tubular furnace is partly closed by an annularcover 28 which is protected by a refractory lining 29. In the cover, acentral opening 30 is provided for the direct passage of the furnacegases into the furnace head. The head itself consists of a stationaryportion 3| and a rotatable portion 32 which rotates with the furnace.

The rotatable portion is composed of a short central pipe 33 throughwhich the furnace gases in the upper end of the furnace escape. Thiscentral pipe is surrounded by an annular space 34, bounded externallyand laterally by the annular member 35 and an extension pipe 36. Thisextension serves to protect the packing between members 31 and 38, thestationary and the rotatable parts, respectively, of the furnace head,from becoming overheated by the furnace gases andA from fouling by dustcarried away by the furnace gases. Connected to the annular space 34 viabranch connections 4I are a pluralityof pipes 40 through which the gasesare withdrawn from parts of the furnace that are remote from thel head.According to thev particular condition any appropriate number of pipes40 may be provided.

The stationary part of. the furnace head consists essentially of anelbowpipe 42 and of the extension bell 43 attached thereto, which dipsinto the liquid or sand seal 44 provided on the In this manner, thestationary portion of the furnace head has suicient play to adapt itselfto the expansion. caused in the furnace by the action of heat.

The elbow pipe 42 of the furnace head isprovided with a manhole 46 and acover for this manhole which can be removed for cleaning purposes. Thefurnace head also carries a charging device 5, consisting of. a feedpipe and a chute extending ,into the furnace. The packing between therotative and the stationary parts 'of the furnace head is preferablyequipped with cooling means. y For example, cooling water may belintroduced at inlet 41 for an annular passage 48 and may be dischargedvia outlet 49. y

The stationary portion 3| of the furnace head is provided witha hood Iwhichflts with a certain amount of play into the central gas exhaust n33and is adapted to be displaced along the longitudinal axis of thefurnace by means of a lever.

mechanism 50. It is to be noted .that a perfect tight t between parts 33and 5I is not necessary since the rotary tubular furnacev will always beoperated in such a way that gases flow through pipe 3,3. f These gasespass through the gap between the pipe 33 and the tubular portion 52 of.the hood 5I into the elbow pipe of thel furnace head to be lead awaytogether with the gases issuing through the annular passage 34. The flowof the gases escaping through the pipe 33 is controlled by adjusting thehood 5| in the pipe 33.

In carrying the 'present method into practice, in a rotary furnace whichis about 2 meters in diameter and 24 meters long, the charge wasincreased from 7.5 tons according to conventional practice to 20 tons byemploying higher bafflel rings. This increased quantity corresponds toabout two-thirds of the daily output when operated in accordance withprior procedures. number of baille ringsremained the same, but the firstring in the upper end of the furnace had a height of 50 mm. and theheight of each of'the succeeding rings was increased uniformly by 50mm., so'that the last ring was 600 mm. high.

.During the roasting, the furnace temperatures were unexpectedly foundto be almost equal throughout the furnace, the temperature being 800 inthe rst zone, 850 C. in the central zone and 800 in the nal zone. Theroasted blends had a sulphur content of about 0.8%. Of course, thetemperatures may be increased to a certain extent which raised thetemperatures to 920" C., 980 C., and 900 C., respectively, in thedifferent zones, andl which vincreased the output to about 36 tons.Naturally, a correspondingly larger quantity of roasting air must beadmitted in this case which raises the gas velocity in the furnace fromabout 1.5 meters per second to about 2.2 meters per second. Since thisvelocity is higher than one which is preferred for the roasting Incontrast to the present process, the roasting y of zinc blends wasconducted in accordance with prior procedures in a conventional rotarytubular furnace which is about 2 meters in diameter, about 24 meterslong, and the baffle rings were arranged in the following manner. In theupper third of the furnace, there were 3 baffle rings about 150 mm. inheight; in the central third 5 rings of the same height; and in thefinal third The 4 rings of the same height. 'Ihe baille rings werespaced at approximately equal distances. Each of the resulting sectionsbetween baffle rings held about 625 kgs. of blends so that the 'totalcharge in the furnace was about 7.5 tons. The output of the furnace perday (24 hours)' was about 30 tons of blends containing' 30% of sulphurand the charge retained in the furnace was equivalent to one fourthofthe daily output. When carrying out the roasting process, atemperature of about 1000 C. was attained in the upper part of thefurnace at which temperature there was a tendency for incrustations tooccur. In the central zone the temperature was around 800 C. and in thelast third of the furnace, it was below 600 C. At these low temperaturesdead-roasting of thezinc blends was naturally impossible. The volume ofgas was estimated at about 80,000 .cubic meters with a sulphur contentof about 6% giving an effective maximum gas velocity of about 1.5 metersper second at a furnace temperature of about 800 C.

Assuming that in a rotary tubular furnace provided with turning devices,the reactions are especially accelerated by the repeated descent of thecharge through the4 gas space of the furnace, the eilcient balance oftemperature realized by the present invention may possibly be explainedin part by the fact that the charge material descending through the gasspace mingles with comparatively large quantities of the materialas soonas it returns to the dominant bed of ore present in the furnace. Theaccelerating effect of the movement of the charge material through thefree spaceV of the furnace is therefore transmitted to a larger amountof material in interior of which the opportunity for a considerable risein temperature is not so great as in shallower layers of material inwhich latter case the material is able to come into more intimatecontact with the furnace gases.

Although the present invention has been described in conjunction withcertain preferred embodiments, it is to be observed that variations maybe resorted to by those skilled in the art Without departing from thescope and spirit of the invention as defined by the appended claims.

The present application is a division of our copending application,Serial No. 743,511, flied on September 11th, 1934, now Patent2,062,869', and entitled A method of conducting chemical andmetallurgical operations in a rotary furnace.

We claim:-

1. A furnace comprising a rotatable shell, a furnace head mounted atleast at one end of said shell, a central passage in the furnace headthrough which gases are withdrawn directly from the furnace, exhaustports situated on the shell, pipes mounted on the shell and connected tosaid exhaust ports, an annular passage in the furnace head connectedwith said pipes, a throttle member in the central passageforco'ntrolling the gas current therein, and a main gas outlet forsimultaneously withdrawing gases from saidcentral and from said annularpassage.

2. A furnace comprising a rotatable shell, a

furnace head mounted at each end of said shell,

each of said heads having a rotatable part attached to the shell,acentral passage in each furnace head through which gases are Withdrawndirectly from the furnace, exhaust ports situated on the shell, pipesmounted on the shell and connected to said ports, an annular passage ineach furnace head connected with said pipes, a throtle member in eachcentral passage for controlling the gas currents and a stationary partfor each of said furnace heads and including a main gas outlet forsimultaneously withdrawing gases from said central and from said annularpassage.

3. A furnace for treating ore comprising a rotary shell, means forfeeding ore to be treated to the interior of said shell, means fordischarging treated ore therefrom, and rings associated with the innersurface of said shell dividing the interior of the furnace into severalsections, the rings in the lower part of the furnace being higher thanthose in the upper part thereof.

4. A furnace for treating ore comprising a rotary shell, means forfeeding, ore to be treated to the interior of said shell, means fordischarging treated ore therefrom, and rings associated with the innersurface of said shell dividing the interior of the furnace into severalsections, the height of said rings increasing from a certain part of thefurnace towards the lower end thereof.

5. A furnace for treating ore comprising a rotary shell, means forfeeding ore to be treated to the interior of said shell, means fordischarging treated ore therefrom, rings associated with the innersurface of said shell dividing the interior of the furnace into severalsections, the height of the rings increasing from a certain part of thefurnace towards its lower end, and a plurality of openings, distributedover the length of the furnace, through which gases are admitted intothe furnace.

6. Afurnace fortreating ore comprising a rotary shell, means for feedingore to be treated to the interior of said shell, means for dischargingtreated ore therefrom, rings associated with the inner surface of saidshell dividing the interior of the furnace into several sections, theheight of the rings increasing from a certain part of the furnacetowards its lower end, and a plurality of openings distributed over thelength of the furheight of the rings increasing from a certain part ofthe furnace towards its lower end, and a plurality of openings,distributed over the length and the circumference of the furnace,through which gases are admitted into the furnace.

8. A furnace for treating ore comprising a rotary shell, means forfeeding ore to be treated to the interior of said shell, means fordischarging treated ore therefrom, and rings associated with the innersurface of said shell dividing the interior of the furnace into severalsections, the height of said rings increasing by steps from one end ofsaid furnace to the other end thereof.

9. A furnace for treating ore comprising a rotary shell, means forfeeding ore to be treated to the interior of said shell, means fordischarging treated ore therefrom, and rings associated with the innersurface of said shell dividing the interior of the furnace into severalsections, the height of said rings increasing by equal steps from. oneend of said furnace to the other end thereof.

10. A furnace for roasting ores comprising a rotary shell, means forfeeding ore to be roasted to the interior of said shell, means fordischarging roasted ore therefrom, and a plurality ofrings spacedlymounted within the interior of said shell and dividing same intosections, said rings having a height increasing from the upper end ofsaid furnace to the lower end thereof and being adapted to retainincreasing charges of ore in the corresponding sections.

11. A furnace for roasting sulphidic ores comprising a shell rotatablymounted in a slightly inclined position, means for feeding ore to beroasted to the interior of said shell, means for discharging roasted oretherefrom, and a plurality of rings spacedly mounted Within the interiorof said shell and dividing same intosections, the height of said ringsincreasing from the upper end of said furnace to the lower end thereofand being so determined that the charge retained in the individualsections defined by said rings will be substantially in inverse ratio tothe speed of the reaction in such section.

CARL PAUL DEBUCH. ERNST MARKWOR'I'H.

